1. Field of the Invention
The subject invention relates to a collapsible, rotatable and expandable spinal hydraulic prosthetic device which may be either implanted within the center of a diseased spinal disk in place of the nucleus pulposis or may replace a degenerated disk altogether. In particular, the present invention directs itself to a spinal prosthesis formed of a bio-compatible metallic bellows, the bellows being filled with a non-compressible fluid. More particularly, this invention directs itself to a spinal prosthesis having the capability of rotating between the two vertebrae adjacent the prosthesis.
Further, the bellows is formed from a plurality of rigid washer-like members, minimizing shear and movement in the lateral direction. Additionally, this invention directs itself to an implantable spinal prosthetic device having an adjustable height, either in vivo or pre-insertion, the height being adjusted to the desired intravertebral spacing of the spine.
2. Prior Art
Implantable spinal prosthetic devices are known in the art. Presently, the primary method employed to remediate degenerative disk disease, discogenic pain or spinal stenosis is through spinal fusion. In this procedure, two or more vertebrae are displaced, the spinal disks between the vertebrae are removed, and crushed bone material taken from the patient""s pelvis is inserted between the two vertebrae. This bone material promotes the growth of new bone in the interstitial space between the vertebrae. Since this growth takes time, some mechanical means must be incorporated at the time of the surgery to rigidly maintain the proper spacing between the vertebrae as well as carry normal ambulatory loads imposed on the spine by the patient. Since the fused vertebrae will no longer take part in normal flexing, higher stress loads will now be imposed on the disks and the vertebrae directly above and below the fused vertebrae.
Commonly used implantable devices include semi-rigid elastomeric filler materials sandwiched between two layers of biocompatible metal. The upper and lower plate surfaces generally have multiple spikes for connection to the vertebrae. Other similar devices offer means to screw the upper and lower plates into their cojoining vertebrae and include treated plates to promote bone growth into them. These devices generally permit a small amount of articulation between the vertebrae, and the longevity of the elastomeric materials and their bonding agents are often quite short. The ideal prosthesis would last 30 to 40 years and withstand two million cycles per year.
It is a purpose of the subject invention to provide a combination of elements making up an implantable spinal prosthesis having both a long life expectancy and providing for total articulation within the spine. More particularly, the subject spinal prosthesis allows for tilting from side to side, front to back, minute elongation and compression along a main axial direction and also rotation of the prosthesis between the two vertebrae about the main axis.
One prior art spinal prosthesis is shown in U.S. Pat. No. 5,002,576. This reference is directed to an intervertebral disk endoprosthesis. This reference teaches a prosthetic device having a central elastomeric layer sandwiched between two cover plates. The prosthetic device is neither rotatable between vertebrae, nor does it provide for sufficient bending in the forward, backward or lateral directions.
Another prior art prosthetic implant is shown in U.S. Pat. No. 4,932,975. This reference is directed to a vertebral prosthesis. The device includes an initially flexible bellows and is made inflexible by injection of a fluid which solidifies and, further, does not allow for rotation between the two vertebrae.
U.S. Pat. No. 3,875,595 is directed to an intervertebral disk prosthesis and instruments for locating the same. The prosthesis is a hollow, bladder-like member having in expanded shape the appearance of the natural nucleus of a natural spinal disk. The device does not allow for rotation between vertebrae, thus not giving the user full articulated movement.
U.S. Pat. No. 5,571,189 is directed to an expandable fabric implant for stabilizing the spinal motion segment. The implant is in the form of an inflatable bag positioned within a cavity artificially formed within the spine. The inflatable bag does not provide for rotation between the vertebrae.
Another prior art prosthesis is shown in U.S. Pat. No. 5,755,807. This reference is directed to an implant module unit and rotating seal for a prosthetic joint. This implant includes a ball-and-socket joint surrounded by a flexible metallic bellows. However, the system is subject to wear and premature failure due to friction and debris particle build-up.
None of the prior art provides for a combination of elements forming a collapsible, rotatable and expandable spinal hydraulic prosthetic device including a flexible metallic bellows which prevents shear-movement in a lateral direction. Additionally, none of the prior art Patents provide for a spinal implant device having a bellows/roller-bearing combination which is rotatable, thus allowing full articulation, between the two vertebrae.
The present invention provides for a collapsible, rotatable and expandable spinal hydraulic prosthetic device which is adapted to be implanted between two vertebrae. The spinal prosthetic device includes a flexible bellows positioned between two roller-bearing assemblies. The radial-thrust bearing assemblies are affixed to vertebra engaging members, respectively, which contact and set the prosthetic device to the vertebrae. The radial-thrust bearing assemblies allow for the bellows to be rotated between the two vertebrae, allowing for rotational articulated movement within the spine.
Further, the bellows is formed from a plurality of rigid washer-like members which prevent shear-movement along a lateral direction. The bellows is filled with a non-compressible fluid and may be adjusted to the desired height either pre-insertion or in vivo.
It is a principle objective of the subject collapsible, rotatable and expandable spinal hydraulic prosthetic device to provide a spinal prosthesis for replacement of a spinal disk.
It is a further objective of the subject spinal prosthetic device to provide a spinal prosthesis having an adjustable axial height.
It is a further objective of the subject invention to provide a spinal prosthesis which rotates between the two adjacent vertebrae.
It is a further objective of the subject invention concept to provide a spinal prosthetic device which prevents shear-movement along a lateral direction.
It is an important objective of the present invention to provide a spinal prosthetic device having a valve assembly allowing for the variable filling of the prosthesis with a mixture of incompressible and compressible fluids, thus allowing for a variable height of the prosthesis between the two vertebrae and also allowing for variable axial compression-movement within the prosthetic segment.
It is a further objective of the present invention to provide a spinal prosthetic device having load bearing capability afforded via a bellows configurational device.
It is an objective of the present invention to provide a spinal prosthetic device having a liquid filled metallic washer convoluted design to permit flexural movement but resist parallel shear movement.
It is a further objective of the present invention to provide a metallic bellows which affords flexing of the convolution elements which mimic natural body movements.
It is an objective of the present invention to provide a bellows design permitting axial height adjustment either pre or post implantation which can be adjusted to precisely fit the patient""s intravertebral space requirement.
It is a further objective of the present spinal implant to provide an extension hose which allows for post operative intravertebral gap adjustments.
It is an additional objective of the present invention to provide a device which can be implanted in the space formerly occupied by the nucleus pulposis whereby the annulus fibrosis is left intact.
It is a further objective of the present spinal implant device to provide a system which can be substituted in place of the entire anatomical disc.
It is an important objective of the present invention to provide a spinal implant with a virtually infinite life expectancy and with no chance of rejection by the body.